OBJECTIVES: MGEN, a health insurance covering mainly teachers in France, is looking to set up a coronary heart diseases (CHD) prevention program in order to reduce CHD mortality, morbidity, and associated costs. However, due to the particular demographics of the covered population, the expected benefits of the program, given the programs parameters, is difficult to foresee. Yet, an estimation of the program effectiveness could help promote the programs importance to decision makers, motivate individuals responsible for the program implementation and encourage patient enrolment. Thus, the objective of this study was to construct a tool that could simulate the effectiveness of CHD prevention based on the demographical characteristics of the target population.  METHODS: We constructed a micro-simulation model that simulated a cohort of individuals participating in a CHD prevention program. Individuals’ baseline characteristics were based on age and sex distribution. CHD risk factors including systolic arterial pressure, body mass index, total cholesterol, smocking, diabetes, stroke and CHD prevalences were fitted by age and sex for the French population. Effectiveness values for CHD prevention programs were based on the COCHRANE review. One-year and ten year CHD mortality were estimated from SCORE and 10 years CHD events from FRAMINGHAM. RESULTS: Implementing a prevention program in a population of a 100 000 representative of the insurance population with a 27% participation rate reduced CHD mortality by 9 after 1 year. The number needed to treat (NNT) was 2988. Excluding individuals with no CHD risk factors reduced NNT to 1571 with a similar mortality reduction. Further excluding participants of 44 years or less reduced NNT to 947 and double the mortality reduction. CONCLUSIONS: The effectiveness and efficiency of a CHD prevention program is sensitive to the target population. Simulation tools are useful to decision makers to better specify the target population in order to optimize the program’s efficiency.